The Validity of Lenke's Criteria for Defining Structural Proximal Thoracic Curves in Patients with Adolescent Idiopathic Scoliosis

Summary: Thirty-seven AIS patients with nonstructural proximal thoracic (PT) curves according to Lenke's criteria were studied and two groups were constructed according to the involvement of PT curve into instrumented fusion. It was found that, according to Lenke's criteria, inclusion or not of the nonstructural PT curve into limits of instrumentation does not change the radiologic outcome. As a result, Lenke's classification is valid and can effectively determine which PT curves need fusion and which do not.

Introcuction: Lenke et al. classified curves of adolescent idiopathic scoliosis (AIS) patients and assigned the term "structural" or "nonstructural" to each curve. However, there is still not much consensus on the definition of structural proximal thoracic (PT) curve, and structurality criteria for PT curve have not been validated, yet. Aim is to delineate the efficiency of using Lenke's criteria during the decision of whether to include the PT curve into instrumented fusion or not in AIS patients.

Materials and Methods: Inclusion criteria: 1-AIS patients treated with a posterior translational instrumentation system, 2-Non-structural upper thoracic curves, 3-A minimum of 2 years of follow-up. Thirty-seven consecutive AIS patients (6 male, 31 female) treated with an average age of 15 years (11-24) and follow-up of 55 months (24-90) were studied. Two groups were constructed: Group I; uppermost extent of the instrumentation either T2 or T3, Group II; uppermost extent of the instrumentation at T4 or lower. Radiographic evaluation included measurement of PT , main thoracic (MT), Thoracolumbar-lumbar (TL-L) curves, sagittal Cobb angles of T2-T5, T5-T12, and T10-L2, right and left coracoid process height difference, clavicle angle, and T1 tilt.

Results: The 2 groups were statistically equivalent in terms of age at operation, followup time, preoperative PT and MT, and their corresponding side bending curve magnitudes, as well as the parameters related to shoulder balance, preoperatively. The 2 groups were also statistically equivalent in terms of immediate postoperative and latest follow-up PT and MT, and parameters related to shoulder balance.

Conclusion: It was observed that Lenke's description for structurality of PT curves can determine which curves need fusion and which do not. Since there was no difference among inclusion of a nonstructural PT curve into fusion or solely fusing the MT curve in terms of outcomes, extension of fusion to T2 or T3 is unnecessary.